Contouring tool having automatic interpolation and extrapolation

ABSTRACT

An apparatus and method for generating a contour automatically based on one or more user-generated contours for a three dimensional (3D) structure. In one aspect, a method of integrating image contour generation and editing with contour interpolation and contour extrapolation is provided. Manual contour drawing and editing may be performed by a user while interpolation and/or extrapolation of contours is automatically calculated in the background. Results of the interpolation and/or extrapolation may be displayed immediately, allowing the user to easily make refinements to any contours, as needed. In one aspect, interpolated and extrapolated contours may be automatically adapted (e.g., recalculated) according to user-modifications of contours.

RELATED APPLICATION

This application is a continuation application of application Ser. No.14/498,928, entitled “Contouring Tool Having Automatic Interpolation andExtrapolation,” filed Sep. 26, 2014, now U.S. Pat. No. 10,013,810,hereby incorporated by reference in entirety.

TECHNICAL FIELD

The present disclosure pertains generally to the field of processingimages and, in particular, generating contours for defining structuresin medical imagery.

BACKGROUND

The usage of medical imaging devices to diagnose and plan treatment forvarious internal ailments is well known. Often, an imaging device suchas an X-ray device, Computer Tomography (CT), or Magnetic ResonanceImaging (MRI) device is used to generate one or more initial scans orimages of the area of interest. Typically, once an image has beenacquired, critical structures (e.g., regions or organs) disposed in thetarget area are specifically identified and marked so that treatment maybe optimally directed. This process may be referred to as“segmentation.” Segmentation of 3D medical images is a very common taskin radiotherapy treatment planning, and is used for defining importantstructures in the image such as organs or tumor volumes. Structures maybe readily apparent in the image (e.g., a bladder in a pelvic image), orthey may not—for example, a therapy planning structure within certainregions of the image not having any corresponding anatomy. Althoughthere are algorithms for automatic detection of some structures, much ofthe segmentation work still has to be done manually, because not allstructures can be found automatically and most automatically detectedstructures require manual correction.

Usually, the 3D volumetric image is loaded into a software environmentand visualized as a stack of parallel 2D images—so-called “image slices”or, more simply, “slices”—wherein a user employs a contouring tool anddraws closed 2D contours in order to define a portion of the structurefor segmentation. Structures may be delineated via, for example, aboundary (e.g., a contour) or an area. The drawing tool may be like apencil, wherein the boundary of an area is drawn in, or alternatively,the drawing tool may be more like a brush, where an area is “painted” bythe tool. Those 2D contours are finally combined to a 3D surface segmentthat describes the boundary of the region of interest.

By contouring in a slice-by-slice approach, a user of a contouring toolis able to define a 3D image structure incrementally. However, userstypically do not draw a contour on each image slice when defining a 3Dstructure—rather, they draw a contour every few slices, leaving a gap inbetween. Then, an interpolation tool is used to interpolate one or morecontours within the gaps. Interpolation reduces the number of sliceswith which a practitioner needs to interact, potentially improving theefficiency of using the contouring tool. After drawing one or morecontours on, for example, every fourth slice of an image, the user canrun an interpolation algorithm to fill the gaps (e.g., generate contourson the intervening planes) and review the result. In addition tointerpolation, some contouring tools provide the functionality ofcontour extrapolation. Extrapolation can generate approximate contourson neighboring slices outside of the range of image slices containinguser-generated contours, e.g., after drawing on one slice the user canrun an algorithm that extrapolates the contours to one or multiple emptyneighboring slices.

However, in conventional image contouring environments, bothinterpolation and extrapolation functions are implemented as separatetools from the contouring tool. Therefore, a user of a conventionalcontouring tool is forced to repeatedly switch between contour drawingand interpolation or extrapolation modes, in order to generate andrefine a 3D structure.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that is further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

In one aspect, embodiments according to the present disclosure providean apparatus and method for generating a contour automatically based onone or more user-generated contours, for a three dimensional (3D)structure. In one aspect, a method of integrating image contourgeneration and editing with contour interpolation and contourextrapolation is provided. Manual contour drawing and editing may beperformed by a user while interpolation and/or extrapolation of contoursis automatically calculated in the background. Results of theinterpolation and/or extrapolation may be displayed immediately,allowing the user to easily make refinements to any contours, as needed.In one aspect, interpolated and extrapolated contours may beautomatically adapted (e.g., recalculated) according touser-modifications of contours.

According to embodiments of the present invention, in one aspect amethod is provided of automatically generating a contour based onuser-generated contours in an image, where the image includes a numberof image planes. The method includes receiving a user input thatcorresponds to at least two user-generated contours. The user-generatedcontours each have a respective image plane, and are nonadjacent to eachother. A computer processor determines a set of image planes that arelocated between the image planes having the user-generated contours. Thecomputer processor automatically generates interpolated contours onplanes with the determined set of image planes, where the interpolatedcontours are based on the user-generated contours.

The foregoing is a summary and thus contains, by necessity,simplifications, generalizations and omissions of detail; consequently,those skilled in the art will appreciate that the summary isillustrative only and is not intended to be in any way limiting. Otheraspects, inventive features, and advantages of the present invention, asdefined solely by the claims, will become apparent in the non-limitingdetailed description set forth below.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention:

FIG. 1 depicts an exemplary graphical user interface (GUI) for acontouring program, displaying orthogonal planar views of image data, inaccordance with embodiments of the present disclosure.

FIG. 2 depicts a side-view of an exemplary contouring sequence, inaccordance with embodiments of the present disclosure.

FIG. 3 depicts a side-view of an exemplary contour editing sequence fora 3D structure, in accordance with embodiments of the presentdisclosure.

FIG. 4 depicts a side-view of an exemplary contouring sequence, inaccordance with embodiments of the present disclosure.

FIG. 5 depicts a side-view of an exemplary contouring sequence, inaccordance with embodiments of the present disclosure.

FIG. 6 depicts steps of an exemplary contour generation process, inaccordance with embodiments of the present disclosure.

FIG. 7 depicts an exemplary computing environment, in accordance withembodiments of the present disclosure.

DETAILED DESCRIPTION

In contrast to conventional approaches, where a user must switch betweenseparate drawing and interpolation/extrapolation tools in order to makeiterative changes when contouring to generate a 3D structure,embodiments of the present disclosure including automatic interpolationand/or extrapolation integrated with a contour-drawing tool enable areduction in trial-and-error contouring procedures.

According to an aspect of the present disclosure image slices may haveplanes arranged in parallel, but arbitrary, orientation in the imagevolume. For example, the image data need not be oriented in thecanonical transverse, coronal, and/or sagittal planes (although theseorientations are consistent with embodiments of the present disclosure).Parallel orientation of image planes enables contour-editing operationsat any point in time. Interpolation and extrapolation algorithms knownto one skilled in the art, such as geometric (e.g., linear, cubic,quadratic, spline-based) and pixel-based (e.g., intensity-based,level-set methods) algorithms, are consistent with embodiments of thepresent disclosure. The systems and processes disclosed herein emphasizethe interaction between a user and the automatic algorithms (e.g.,interpolation and/or extrapolation) without requiring a specificalgorithm implementation. Furthermore, embodiments of the presentdisclosure naturally extend the well-known 2D “slice-by-slice”contouring approach to segmentation, and thus may be well-suited to lessexperienced segmentation users.

In some embodiments, the term “image” or “medical image” may be usedinterchangeably and refers to an image created by an imaging system,which includes but is not limited to x-ray radiography, X-ray computedtomography (CT) imaging, magnetic resonance imaging (MRI), positronemission tomography (PET) imaging, single photon emission computedtomography (SPECT) imaging, and ultrasound (US) imaging. A medical imagecan be either a 2D image or a 3D image. However, the system and methodsherein are not limited to medical imaging, but may be applied in anydrawing environment where 3D shapes are constructed by 2D drawing, suchas 3D model construction, computer aided design, and relief generationin geographic systems.

Reference will now be made in detail to several embodiments. While thesubject matter will be described in conjunction with the alternativeembodiments, it will be understood that they are not intended to limitthe claimed subject matter to these embodiments. On the contrary, theclaimed subject matter is intended to cover alternative, modifications,and equivalents, which may be included within the spirit and scope ofthe claimed subject matter as defined by the appended claims.

Furthermore, in the following detailed description, numerous specificdetails are set forth in order to provide a thorough understanding ofthe claimed subject matter. However, it will be recognized by oneskilled in the art that embodiments may be practiced without thesespecific details or with equivalents thereof. In other instances,well-known methods, procedures, and components, have not been describedin detail as not to unnecessarily obscure aspects and features of thesubject matter.

Portions of the detailed description that follows are presented anddiscussed in terms of a method. Although steps and sequencing thereofare disclosed in figures herein (e.g., FIG. 6) describing the operationsof this method, such steps and sequencing are exemplary. Embodiments arewell suited to performing various other steps or variations of the stepsrecited in the flowchart of the figure herein, and in a sequence otherthan that depicted and described herein.

Embodiments described herein may be discussed in the general context ofcomputer-executable instructions residing on some form ofcomputer-usable medium, such as program modules, executed by one or morecomputers or other computing devices. Generally, program modules includeroutines, programs, objects, components, data structures, etc., thatperform particular tasks or implement particular abstract data types.The functionality of the program modules may be combined or distributedas desired in various embodiments.

By way of example, and not limitation, computer-usable media maycomprise computer storage media and communication media. Computerstorage media includes volatile and nonvolatile, removable andnon-removable media implemented in any method or technology for storageof information such as computer-readable instructions, data structures,program modules or other data. Computer storage media includes, but isnot limited to, random access memory (RAM), read only memory (ROM),electrically erasable programmable ROM (EEPROM), flash memory or othermemory technology, compact disk ROM (CD-ROM), digital versatile disks(DVDs) or other optical storage, magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices, or any othermedium that can be used to store the desired information.

Communication media can embody computer-readable instructions, datastructures, program modules or other data in a modulated data signalsuch as a carrier wave or other transport mechanism and includes anyinformation delivery media. The term “modulated data signal” means asignal that has one or more of its characteristics set or changed insuch a manner as to encode information in the signal. By way of example,and not limitation, communication media includes wired media such as awired network or direct-wired connection, and wireless media such asacoustic, radio frequency (RF), infrared and other wireless media.Combinations of any of the above should also be included within thescope of computer-readable media.

Exemplary Contouring Graphical User Interface

With reference now to FIG. 1, an illustration of an exemplary contouringgraphical user interface (GUI) drawing workspace 100 is depicted, inaccordance with an embodiment of the present disclosure. Drawingworkspace 100 provides a software environment in which a user can viewand manipulate images having a plurality of 2D planes (e.g., imageslices) that together form a 3D volume, e.g., medical images. Usingwell-known techniques, users can navigate from slice-to-slice andviewing plane-to-viewing plane within drawing workspace 100 for a givenimage. Drawing workspace 100 comprises a main display 105, the maindisplay 105 showing an image slice with which a user is able tointeract. Also shown is an exemplary drawing tool 110 with which theuser may enter contours on the displayed image slice. An exemplarycontour 115 is shown, drawn on the image slice by the user. For example,the user is able to enter a contour using drawing tool 110. Whiledrawing tool 110 is shown as a pencil, the drawing tool 110 may changeappearance and functionality according to user selection, and is able togenerate and edit contours through 2D contour generation means known toone skilled in the art, including a drawing pencil, a paintbrush,polygon or curve tools, and others. The user may be able to edit acontour via, for example, grabbing part of the contour 115 line andpulling with the drawing tool 110. Alternatively, the drawing tool 110may serve to trim the contour 115. Further embodiments provide thecapability of drawing additional lines and/or contours and merging withan existing contour.

Although not shown, drawing workspace 100 may include toolbars havingoptions for displaying and controlling various aspects of the drawingworkspace 100. These may include control of a mode of the drawing tool110, a mode of contouring tool operation (e.g., interpolation,extrapolation, a combination of interpolation and extrapolation),navigation within an image volume, image selection, etc. The drawingworkspace 100 may include additional views, as shown in FIG. 1. Forexample, the drawing workspace 100 may display a view corresponding tothe transverse viewing plane 150, a view corresponding to the coronalviewing plane 160, and a view corresponding to the sagittal viewingplane 170. However, views of drawing workspace 100 are not limited totransverse, coronal, and sagittal viewing planes.

These additional views may be, for example, useful for displaying anoverview of the image data and the defined contouring for the loadedimage. Additional views may display, for example, a set of slices of theimage volume, projections such as digitally reconstructed radiographscorresponding to various viewing angles, or 3D views. For example,coronal plane 160 depicts overview display 120 showing a pelvic area ofa patient. The display 120 includes a side-view of a 3D structure 125,which is defined by a plurality of 2D contours that have been definedusing the display 105. The display 120 indicates a current contour 130in bold, a feature which may be used to distinguish the current imageplane 135 (which may be indicated via, e.g., a set of arrows at theedges of the display 120) from other image planes. Furthermore, contoursmay be displayed differently according to their origin, that is,user-generated contours may be displayed differently from interpolatedand/or extrapolated contours, as discussed in further detail below. Thepositions of planes of the plurality of image planes may be indicated bylines 140, located at the edge of display view 120. Embodiments of thepresent disclosure include various layouts, combining one or moredrawing displays with zero or more overview displays.

Typically, if a scanning device is used to generate the image data, thescanning device generates images in slices that are orthogonal to theZ-axis (e.g., the transverse plane 150). However, an image may begenerated from the original image data in any orientation, that is, the“planes” of the image need not be orthogonal to the Z-axis, and/orco-planar with the slice data generated by the scanning device. This isbecause the image dataset may be manipulated ex post facto in order toview image slices at arbitrary plane angles. In other words, the imagedata can be visualized in 3D and freely rotated, and parallel planes maybe defined at an arbitrary angle. Image data, which are sampled in someway (e.g., a voxel grid) having three coordinate axes, may bedynamically re-sampled to form new image slices. These image slices,however, should be parallel to one another, in order to enablecalculation of interpolation and/or extrapolation of contours at anytime (e.g., during an initial contouring session, and/or at a subsequentsession for the same image data). Typically, the distance between imageslices is approximately between 1-2.5 mm, although other values for thedistance between parallel image slices are consistent with the spiritand scope of the present disclosure. The distance between image slicesmay be directly tied to the distance between slices generated viaimaging device (e.g., based upon imaging system resolution). Or, thedistance between image slices may be virtually determined if imageplanes are defined by image dataset (e.g., not directly from scanningdata), in which case a step-size is set for the distance between planesin the virtualized image data.

Manual Contour Generation with Integrated Interpolation

In one aspect, embodiments of the present disclosure provide acontouring tool wherein a user may define a contour on a first imageslice, skip several slices, and by defining a second contour (at theremote slice) the contouring tool will respond by performing automatedinterpolation on planes between the two user-defined contours. A featureof the present disclosure includes automatic interpolation of contourson image planes located between nonadjacent image planes on which a userhas manually defined contours, effectively “filling the gaps” while auser is drawing contours. Interpolation distance (e.g., the number ofimage slices) may be varied according to user selection, e.g., in viewof the complexity of the structure to be delineated, which may bedetermined according to which image slices are selected for manualcontour entry. For example, a simple geometry may enable a larger numberof slices to be skipped by a user performing the contouring, andtherefore a larger number of interpolated slices. Conversely, a morecomplex geometry may require fewer skipped contours, so that theinterpolation does not fail attempting to resolve a too-large change incontour shape over a large distance.

FIGS. 2-5 are illustrations of exemplary contour generation sequences togenerate a 3D structure in an image, in accordance with embodiments ofthe present disclosure. FIG. 2-5 are depicted using a side-view of therespective contouring sequences. While a side-view is not typically theview used for generation of the contour(s), for purposes of clarity thecontouring processes integrating interpolation and/or extrapolation aredepicted in this manner. In practice the view employed by a user tointeract with the contouring tool in order to generate the contour(s) isoften a top-down view, e.g., drawing view 105 of FIG. 1.

FIGS. 2-5 each include a vertical dashed line. At the left side of thevertical dividing line of FIGS. 2-5 is the sequence of user inputs forcontours (e.g., contour generation or edit), and at the right of thedividing line the corresponding result for each user input. In anembodiment of the present disclosure, the corresponding result shown atthe right side occurs after automatic calculation (e.g., by processor701 of computing system 700 in FIG. 7) following the user input. Theautomatic calculation may occur immediately following cessation of theuser input, e.g., as soon as the user completes generation of a closedcontour and ceases to interact with the contour generation tool (a toolsuch as a drawing pencil, or paintbrush).

Referring now to FIG. 2, a contouring sequence 200 comprises steps201-204. At step 201 a user generates, via a manual input, a contour 205on a single image plane of a plurality of image planes 210, theplurality of image planes corresponding with 2D image slices of animage. The manual input may be made with any suitable 2D drawing toolknown to one skilled in the art, e.g., drawing tool 110 of FIG. 1 whichmay include paintbrushes, polygon or curve tools, deformation tools, oradaptive tools like active contours. The right side of FIG. 2 at step201 shows no change from the left side, as there is no need forinterpolation with only the one contour 205 defined. A minimum number oftwo (2) user-generated contours must be defined in order for thecontouring tool to perform interpolation.

At step 202 the user generates a second contour 215 at a lower imageplane (e.g., skipping 4 image planes). Following the user inputcompleting contour 215, shown at the right side of FIG. 2, the systemautomatically interpolates contours on the image planes in a region 225,the region 225 comprising image planes located between the image planeof contour 205 and the image plane of contour 215. Those planes serve asboundary conditions for the interpolation, but contours on those planes(e.g., 205 and 215) are not modified by the interpolation, in order notto alter the user-made contours. A representative interpolated contour220 is shown within the interpolation region 225. The two user generatedcontours 205 and 215, along with the interpolated contours within region225, form a 3D structure 230 in the image.

At step 203 the user enters a third user-generated contour 235, belowthe other contours. At the right, the result of the automaticinterpolation is additional contour interpolation in a region 240, theregion 240 comprising image planes located between the new contour 235and the nearest user-generated contour, contour 215.

A feature according to embodiments of the present disclosure is targetedinterpolation of just a portion of the contours comprising the 3Dstructure. Embodiments of the present disclosure provide a system andmethod that remembers and distinguishes contours that are user-definedfrom those that are interpolated and/or extrapolated. The contouringtool uses this information to determine the region over whichinterpolation and/or extrapolation will be performed. A user is able torefine the shape of a generated 3D structure by editing any contour inthe 3D structure (e.g., either a user-generated contour or aninterpolated contour), and the contouring tool will generate (or update)the 3D structure by calculating (or recalculating) interpolated contoursonly on planes between the edited contour and the nearest user-generatedcontour(s). Therefore, at step 203 the system automatically interpolatesonly contours on planes within region 240, generating an updated 3Dstructure 230′.

At step 204 a user has navigated back through image planes 210, andenters an edit to a formerly interpolated contour, forming a newuser-generated contour 245. The user may edit the contour by reshapingthe interpolated contour (or contours) of that plane, or by deleting theinterpolated contour and entering a new contour. At the right the systemautomatically recalculates interpolation in order to update the 3Dstructure, forming updated 3D structure 230″. Specifically,interpolation is recalculated only for contours within regions 250 and255, which comprise those planes between the plane having the useredited contour 245 and the planes having the nearest user-generatedcontours—in this case, planes having contours 205 and 215. Interpolationis not performed again for region 240, since there have been no changesto the user-generated contours (215 and 235) upon which the interpolatedcontours of region 240 are based. This feature of the present disclosureminimizes the region(s) that need interpolation following user contourgeneration and/or editing.

With interactive, integrated interpolation, one can adapt dynamically tothe 3D structure generated via contouring. At any time, a user is ableto skip however many slices are desired, and following user-generationof contours the user will see the interpolation result visualizedshortly thereafter. Again, a user need not adhere to a specific numberof image slices to skip. For example, the user in the example of FIG. 2initially skips 4 image slices between user-generated contours 205 and215, and then 2 slices between 215 and 235. The contouring tool mayinterpolate contours just on the image slices between the newlygenerated contour and the closest one or two slices havinguser-generated contours. This enables a user to skip over regions ofrelatively simple geometry, and to define with more user input (e.g., agreater number of user-generated contours) regions with greatercomplexity. Furthermore, a user is able to refine the shape of thegenerated 3D structure by selecting and editing any contour within the3D structure. Additionally, contours may be displayed differentlyaccording to their origin, that is, user-generated contours (e.g.,contours 205, 215, 235, 245) may be displayed differently frominterpolated and/or extrapolated contours (e.g., contour 220, contoursin regions 225, 240, 250, 255). For example, user-generated contours mayhave a different line type, thickness, color, or other feature thatclearly distinguishes from interpolated line types. Such information maybe shown both in the main drawing display (e.g., display 105 of FIG. 1)and in the overview displays (e.g., display 120 of FIG. 1).

Depending on the desired shape of the 3D segment, the user may drawmultiple contours on the same slice plane. In such cases theinterpolation may be calculated after each edit of a single contour. Asa consequence the algorithm may also create interpolated slices withmultiple contours. If the user then modifies a single one of thoseinterpolated contours, all contours on the same slice plane are markedas being edited and included in the boundary conditions of the followinginterpolation step.

Moreover, there are no constraints on the interpolation and/orextrapolation algorithms used by the contouring tool described byembodiments herein. Algorithms may be purely geometric, such as linear,cubic or spline-based methods, or they can incorporate the underlyingpixel data, like level set methods or any other available data such asphysical or anatomical models. In an embodiment of the presentdisclosure, the contouring tool performs calculation of interpolatedcontours according to several different algorithms in parallel. In theseembodiments, the contouring tool may present a preview of theinterpolated contours according to each algorithm, and the user is ableto select those contours generated by the algorithm giving the bestmatch with the 3D structure being defined. In an embodiment the user isable to select one or more algorithms that will be used to generate theinterpolated and/or extrapolated contours.

Referring now to FIG. 3, a contouring process 300 for editing a 3Dstructure is depicted, process 300 having steps 301-304. Step 301 doesnot begin with a user input of a contour, but rather a pre-existing 3Dstructure 330 is shown, along with a representative contour 305. The 3Dstructure 330 shown at step 301 may be via, for example, a priorcontour/interpolation session, or some other process (such asauto-segmentation, wherein a user is not defining the structuremanually). While 3D structure 330 is comprised of multiple image slices,initially 3D structure 330 has no user-defined contours, as there havebeen no contours defined by a user during the current structure editingsession. The structure 330 may have been defined during a prior session(e.g., the contouring/interpolation process 200 in FIG. 2, above). Forexample, the structure 330 may be from a predefined case of segmentationfrom a database of the contouring system, or from another database. Inan embodiment according to the present disclosure, contours are definedas user-generated only for a given session of a contouring tool.Contours that were user-defined and were the basis for interpolation (orextrapolation, described below) in an earlier session are now displayedand treated identically to the interpolated planes in a later session.In other words, all of the contours of a pre-defined 3D structure mayinitially be treated identically by the contouring tool at the start ofan editing session.

At step 302 the user inputs an edit to a contour 310. The result of theuser input is a change in the display of the contour (e.g., it may nowbe displayed in bold), and the 3D structure 330 has updated that contourand now forms 3D structure 330′. Note that no interpolation hasoccurred, as there is only one user-defined contour at this point.

At step 303 the user inputs an edit at a lower plane, generating contour315. This automatically results in a change in the display of thecontour 315, as well as the determination of a region 325 over whichinterpolation is performed. The region 325 includes planes between thoseplanes having contours 310 and 315, and the interpolation results ininterpolated contours on the planes of region 325. As shown, a userediting the lower contour (contour 315) leads to interpolation for theregion above (region 325), up to the next user-defined contour (contour310), but not for the region below, because there is no user-definedcontour below the currently edited contour (contour 315). Contour 320 isan exemplary interpolated contour within region 325. The user-generatedcontours 315 and 315, along with the interpolated contours of region325, form 3D structure 330″. In an embodiment of the present disclosure,a region for interpolation (or extrapolation) may be indicated visuallyto a user, via for example shading of the region or varying linethicknesses in the display area.

At step 304 a user performs an edit of a contour within the interpolatedregion of step 303. This edit generates contour 335. In response to theuser edit, the 3D structure is automatically updated. In particular,regions 340 and 345 are determined to include planes for interpolation,and the interpolation of contours on the planes of regions 340 and 345generates updated 3D structure 330.′″ The regions 340 and 345 aredetermined because the edited contour 335 has user-defined contours bothabove (contour 310) and below (contour 315), and therefore interpolationis performed for regions both above (region 340) and below (region 345).

According to an embodiment of the present disclosure, the interpolationof contours 325 can be further refined by an autosegmentation tool in acase where a user skips several planes between manual edits of contours(e.g., contours 310 and 315). The autosegmentation tool is able toinsert segmentation data for each of the skipped planes, resulting incontours that are manually defined (via user-edit) at 310 and 315, andcontours that are generated via autosegmentation for contours 325.According to an embodiment, the user can subsequently edit one or moreof the autosegmented contours 325. A combination of manual edits,interpolation, and autosegmentation is possible, such that contours ofthe segment may include those that are automatically interpolated,automatically interpolated with subsequent manual edit, autosegmented,and autosegmented with manual edit.

Manual Contour Generation with Integrated Extrapolation

In image segmentation, volumes defined within an image are typicallyirregular in shape. For such an image, with regard to contouring,copying of an initial contour from one plane onto adjacent planes can beuseful. For a 3D segment defined in a plane-by-plane manner,extrapolation can be useful to define a contour, which can either beedited or discarded (but in either case, should speed up userinteraction in the contouring procedure). Conventionally, a contouringtool including extrapolation functionality incorporates extrapolation ina piecemeal fashion, that is, each extrapolation process must beincrementally applied after each manual entry of contours. According toan aspect of the present disclosure, extrapolation functionality isintegrated with the contour generation tool, and following manualcontouring of an initial plane, the next plane accessed is automaticallypopulated by an extrapolated contour. This contour may be initially‘proposed,’ allowing the user to accept the proposed contour as-is, orto edit the contour before proceeding to the next plane.

In an embodiment of the present disclosure, extrapolation of contoursproceeds in a plane-by-plane fashion. FIG. 4 illustrates a contouringsequence 400 comprising steps 401-404. At step 401 the user defines afirst contour 405 on one plane from a plurality of image planescorresponding with 2D image slices of the image. In response to the userinput, the system proposes extrapolated contours 410 on the planes aboveand below the plane of the user-defined contour 405.

At step 402 the user accepts the top proposed contour, generatingcontour 415. At the right side, the system in response forms a 3Dstructure 430, comprising the first user generated contour 405 and theaccepted extrapolated contour 415. Furthermore, a contour 420 isautomatically extrapolated on the plane above that of the newly acceptedcontour 415.

At step 403 the user accepts the remaining proposed extrapolated contourof the extrapolated contours 410 at step 401. Note that at step 403 theuser, in accepting the proposed contour, has made an edit to thecontour, generating a contour 425 having a different shape than thecontour initially proposed via extrapolation. In response the 3Dstructure 430 is updated, forming 3D structure 430′. Additionally, anewly proposed contour 440 is automatically extrapolated on the adjacentplane.

Step 404 illustrates a user-edit of an inner contour of the 3Dstructure. For an extrapolation process, a user edit of an inner contour(e.g., not at the top or bottom of the currently defined structure), maynecessitate an update to the proposed extrapolated contours, in order toaccount for the new shape of the segment. Therefore, embodimentsaccording to the present disclosure provide the capability of updatingmore extrapolated contours than just those on the immediatelyneighboring planes of the edited contour. At step 404 a user edit ofshifting the center contour to the left generates contour 405′. Inresponse, a change is made to the contours, updating the 3D structure430′ to 3D structure 430″, and proposed extrapolated contours 420 and440 to updated proposed extrapolated contours 420′ and 440′.

The shape of the proposed, extrapolated contours shown in FIG. 4 may bebased on, for example, linear extrapolation. Alternatively, theextrapolation methods may be pixel-adaptive, methods which areparticularly well-suited to shapes visible on the image (e.g., anatomysuch as bladder, bone). Defining 3D structures for other kinds ofshapes—such as volumes for radiation planning, which are not visible onthe image and are therefore not suitable for pixel-adaptivealgorithm—may require alternative extrapolation methods. The simplestextrapolation method may be to simply copy the shape of one contour toan adjacent contour on a plane above and/or below.

As discussed above, a feature of contouring tools according to thepresent disclosure is that extrapolated contours are proposed (e.g.,suggested), rather than being, for example, system-defined with acapacity for user edit afterward. This is due to the fact that, when acontour is proposed only, a user must accept it in order to instantiatethe contour. The acceptance may be either through applying the proposedcontour as-is, or through editing of the proposed contour. When thedrawing tool function is ended, any remaining suggested contours may notbe applied. In this manner, contouring is completed at thecurrently-selected plane, rather than at an adjacent plane (which theuser may not be viewing, or interested in). As described above, proposedcontours may appear as semi-transparent, dashed, or some other displayedline or indicia that is differentiated from the user-defined contours.In an embodiment, once the contouring tool is turned off the proposedcontour lines are no longer displayed, as they are a part of thevisualization of the contouring tool, not part of the defined 3Dsegment.

Depending on the desired shape of the 3D segment, the user may drawmultiple contours on the same slice plane. In such cases theextrapolation may be calculated after each edit of a single contour. Asa consequence the algorithm may also create extrapolated slices withmultiple preview contours. In an embodiment, if the user then accepts ormodifies a single one of those preview contours, all preview contours onthe same slice plane are added to the 3D segment before theextrapolation algorithm is run again.

Manual Contour Generation with Combined Interpolation and Extrapolation

Interpolation and extrapolation functionality need not be implemented asseparate features for a contouring tool, according to embodiments of thepresent disclosure. As an extension of the process 400 described in FIG.4, the extrapolation of contours is able to be made for more than oneboundary slice on each side of a user generated contour. In anembodiment, the extrapolated contours are suggested on all remainingslices of the image, up to the volume boundaries. In such cases the usermay accept, for example, any one or more of the extrapolated slices,such that all slices located between the current plane and the existing3D segment are added to the 3D segment. Furthermore, if a contour isimplicitly accepted by the user via editing, any intermediate contours(e.g., between the existing user-generated contour and/or defined 3Dsegment) may be adapted via interpolation, and then added to the 3Dsegment.

FIG. 5 illustrates a contouring process 500 comprising steps 501-503, inwhich a combination of automatic interpolation and extrapolationfunctions are integrated with manual contour entry by a user of thecontouring tool. At step 501 a user inputs a first contour 505 on afirst image slice. At the right, a plurality of extrapolated contours510 is generated in response to contour 505. The extrapolated contoursare formed on several neighboring image planes both above and below theplane having contour 505, and may include all image planes included inthe image volume. According to an embodiment of the present disclosure,a user is able to specify the number of neighboring image planes onwhich extrapolated contours will be formed.

At step 502 a user accepts, several slices above contour 505, one of thesuggested extrapolated contours, forming contour 515. In response, a 3Dsegment 530 is generated, which includes contours 505 and 515, as wellas the (formerly) suggested extrapolated contours 520 on those planes inbetween the ones of contours 505 and 515.

At step 503 the user accepts, several slices below contour 505, anedited suggested extrapolated contour, forming contour 525. In response,3D segment 530′ is generated. Due to the user edit of the initialsuggested extrapolated contour 510, the contours within region 540 arealtered; more specifically, an interpolation is performed between theuser-generated contours 505 and 525 (which form the boundary conditionsof the interpolation). Furthermore, the extrapolation is updated,generating extrapolated contours 510′ on the planes below contour 525.

The order of operation for interpolation and extrapolation functionswith the contouring tool may be varied. In one case, first interpolationis performed, and then extrapolation accounts for the current set ofuser-defined contours. In another case, extrapolation is performedfirst, and then interpolation is performed based on user-definedcontours.

FIG. 6 depicts a flowchart 600 of a method of generating a contour foran image having a plurality of image slices (e.g., 2D image planesdefining a 3D image volume), in accordance with embodiments of thepresent invention. Contouring may be performed for an image in order todefine a 3D structure of interest within the image.

The steps 601-605 describe exemplary steps comprising the processdepicted in flowchart 600 in accordance with the various embodimentsherein described. In one embodiment, the flowchart 600 is implemented ascomputer-executable instructions stored in a computer-readable mediumand performed by a computing device (e.g., such as computing device 700of FIG. 7) executing a process for contouring an image to define imagestructures of interest, for example, for a 3D segment in a medicalimage.

At step 601 user input is received, corresponding to a first contourgenerated by the user. The first contour is defined on a first plane(e.g., image slice) of the image. The user input may be received througha graphical user interface of the software application (e.g., drawingworkspace 100 of FIG. 1). In an embodiment the user input correspondswith one closed contour on the image slice. In an embodiment the userinput corresponds to multiple closed contours, all located on the sameimage slice.

At step 603 a determination is made of which image planes of the imageare located neighboring the plane having the first contour. These planesform a first image planes set. In one embodiment the image planesincluded in the first image planes set are the immediately adjacentplanes to the plane having the first contour (e.g., one plane above, andone plane below the plane having the first contour). In an embodiment, aplurality of neighboring planes is included in the first image planesset (e.g., several planes above, several planes below the plane havingthe first contour). In an embodiment, all planes in the image volume areincluded in the first image planes set.

At step 605 the computing system automatically generates one or morecontours for planes included in the first image planes set. In anembodiment, the automatically generated one or more contours areimmediately added to the first user-generated contour, generating orextending a 3D structure in the image volume. In an embodiment, the oneor more contours are proposed (e.g., displayed as suggestions), andrequire further user input (e.g., accepting as-is, or via editing) priorto inclusion in the 3D structure that is being defined by the userduring the contouring session. The one or more contours may be generatedusing interpolation, extrapolation, or a combination of bothinterpolation and extrapolation. The shape of the contours and theirlocation within respective planes are based on the shape and location ofthe first user-generated contour.

According to an embodiment of the present disclosure, interpolation ofcontours may be combined and/or cross-referenced (e.g., based oncomparison of two or more image segments). For example, a first imageplanes set can be based on x-y plane slices along a z-axis of a 3Dvolumetric image. A first segmentation data is generated by a process asdescribed herein (e.g., manual entry of user-generated contours,interpolation and/or extrapolation of contours at neighboring planes). Asecond image planes set is then generated based on plane slices at adifferent orientation in the image volume—for example, x-z plane slicesalong the y axis of the 3D volumetric image. A second segmentation datais likewise generated by a process as described herein (e.g., manualentry of user-generated contours, interpolation and/or extrapolation ofcontours at neighboring planes). Thereafter, the processor is able toaccess the first segmentation data and reference the contour from thesecond segmentation data in order to modify the first segment—forexample, to make corrections to the segment. Alternatively, segmentationmay be performed on the first image planes set and on the second imageplanes set, independently, and subsequent interpolation and/orextrapolation is able to be applied via cross-referencing both imageplanes sets. While the two image planes sets thus described areperpendicular, this is not a requirement of the present embodiment.

Exemplary Computing Device

As presented in FIG. 7, an exemplary system upon which embodiments ofthe present invention may be implemented includes a general purposecomputing system environment, such as computing system 700. In its mostbasic configuration, computing system 700 typically includes at leastone processing unit 701 and memory, and an address/data bus 709 (orother interface) for communicating information. Depending on the exactconfiguration and type of computing system environment, memory may bevolatile (such as RAM 702), non-volatile (such as ROM 703, flash memory,etc.) or some combination of the two. In some embodiments the memory issubstantially radiation-hardened, using substrates and/or logicalmethods known to those skilled in the art.

Computer system 700 may also comprise an optional graphics subsystem 705for presenting information to the computer user, e.g., by displayinginformation on an attached display device 710, connected by a videocable 711. According to embodiments of the present disclosure, thegraphics subsystem 705 may be coupled directly to the display device 710through the video cable 711. A graphical user interface of an imageviewing software application executing in the computer system 700 may begenerated in the graphics subsystem 705, for example, and displayed tothe user in the display device 710. For example, the graphics subsystem705 may present a graphical user interface (GUI) including a contouringtool according to embodiments of the present disclosure, such as GUI 100of FIG. 1. In alternate embodiments, display device 710 may beintegrated into the computing system (e.g., a laptop or netbook displaypanel) and will not require a video cable 711.

Additionally, computing system 700 may also have additionalfeatures/functionality. For example, computing system 700 may alsoinclude additional storage (removable and/or non-removable) including,but not limited to, magnetic or optical disks or tape. Such additionalstorage is illustrated in FIG. 7 by data storage device 704. Computerstorage media includes volatile and nonvolatile, removable andnon-removable media implemented in any method or technology for storageof information such as computer readable instructions, data structures,program modules or other data. RAM 702, ROM 703, and data storage device704 are all examples of computer storage media.

In an embodiment, computer system 700 comprises instructions forperforming processes according to aspects of the present disclosure,where the instructions may be stored on RAM 702, ROM 703, and/or datastorage 704. For example, the computer system 700 may comprise automaticcontour generation instructions 713, where automatic contour generationinstructions 713 contain instructions causing computer system 700 toperform a process of generating one or more contours automatically fromuser-generated contour(s), according to embodiments of the presentdisclosure (e.g., processes 200, 300, 400, 500, 600).

Computer system 700 also comprises an optional alphanumeric input device706, an optional cursor control or directing device 707, and one or moresignal communication interfaces (input/output devices, e.g., a networkinterface card) 708. Optional alphanumeric input device 706 cancommunicate information and command selections to central processor 701.Optional cursor control or directing device 707 is coupled to bus 709for communicating user input information and command selections tocentral processor 701. Signal communication interface (input/outputdevice) 708, also coupled to bus 709, can be a serial port.Communication interface 709 may also include wireless communicationmechanisms. Using communication interface 709, computer system 700 canbe communicatively coupled to other computer systems over acommunication network such as the Internet or an intranet (e.g., a localarea network), or can receive data (e.g., a digital television signal).

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.The subject matter is not limited to medical imaging, but may be appliedin any drawing environment where 3D shapes are constructed by 2Ddrawing, such as 3D model construction, computer aided design, andrelief generation in geographic systems. The specific features and actsdescribed above are disclosed as example forms of implementing theclaims.

What is claimed is:
 1. A computer-implemented method of automaticallygenerating a contour based on user-generated contours for defining athree-dimensional (3D) structure in an image, the method comprising:accessing a first user-generated contour and a second user-generatedcontour having a first image plane and a second image plane,respectively, wherein the first and second image planes are nonadjacenthaving at least one image plane disposed between the first and secondimage planes; determining, by a computer processor, a first image planesset comprising image planes disposed between the first and second imageplanes; automatically generating and displaying, by the computerprocessor, an extrapolated contour on a third image plane that isseparated from the first and second image planes and the first imageplanes set therebetween by a second image planes set comprising at leastone image plane; and automatically generating, by the computerprocessor, interpolated contours on planes comprised by the second imageplanes set, the interpolated contours being based on the extrapolatedcontour.
 2. The method according to claim 1, further comprising:receiving user input corresponding to a selection of an interpolatedcontour; receiving user input corresponding to a user modification ofthe interpolated contour; and automatically updating, by the computerprocessor, interpolated contours in the first image planes set disposedbetween the user-modified interpolated contour and the firstuser-generated contour and between the user-modified interpolatedcontour and the second user-generated contour, wherein the updating isbased on the user-modified interpolated contour and the first and seconduser-generated contours.
 3. The method according to claim 2, wherein theuser modification comprises deletion of the interpolated contour andgeneration of a new contour.
 4. The method according to claim 1, whereinthe first and second user-generated contours are displayed with adifferent visual appearance than the interpolated contours.
 5. Themethod according to claim 1, wherein a selection of different versionsof the interpolated contours is provided, wherein the different versionsare based on different interpolation algorithms.
 6. The method accordingto claim 1, wherein the image planes comprised by the first image planesset are displayed with a different visual appearance than otherdisplayed image planes.
 7. The method according to claim 1, furthercomprising: receiving user input corresponding to a third user-generatedcontour, the third user-generated contour having a corresponding imageplane, wherein the third image plane is nonadjacent to at least one ofthe first and second image planes; determining, by the computerprocessor, a third image planes set comprising image planes disposedbetween the third image plane and the at least one nonadjacent first andsecond image planes; and automatically generating, by the computerprocessor, third interpolated contours on planes comprised by the thirdimage planes set, wherein the third interpolated contours are based onthe first, second, and third contours.
 8. The method according to claim1, wherein the first image plane is parallel with the second imageplane.
 9. The method according to claim 1, further comprisingdetermining distances between the image planes disposed between thefirst and second image planes, wherein an interpolation distancecorresponding to an extent to which the user-generated contours areinterpolated through the planes comprised by the first image planes setis based on a complexity of a geometry of the user-generated contoursand the distances between the image planes in the first image planes setand the first and second image planes.
 10. The method according to claim9, wherein the determining distances between the image planes disposedbetween the first and second image planes comprises using a step-size asa distance between image planes for virtualized image data.
 11. Themethod according to claim 10, wherein the distance is approximatelybetween 1 mm and 2.5 mm.
 12. A computer-implemented method ofautomatically generating a contour based on a user-generated contour fordefining a 3D structure in an image, the method comprising: accessing afirst user-generated contour, the first user-generated contour having acorresponding first image plane; determining, by a computer processor, afirst image planes set comprising image planes comprising a second imageplane and a third image plane separated by the first image plane;automatically generating and displaying, by the computer processor,extrapolated contours on the first image planes set, the extrapolatedcontours being based on the first user-generated contour; andautomatically generating, by the computer processor and based on theextrapolated contours, interpolated contours on image planes between thefirst and third image planes and interpolated contours on image planesbetween the second and third image planes.
 13. The method according toclaim 12, further comprising: receiving user input corresponding to aselection of a contour; receiving user input corresponding to a usermodification of the selected contour; and automatically updating, by thecomputer processor, the extrapolated contours, wherein the updating isbased on the user modification of the selected contour, and theuser-generated contours; wherein the selected contour is one of auser-generated contour and an accepted contour.
 14. The method accordingto claim 12, wherein the number of image planes in the first planes setis variable.
 15. The method according to claim 12, wherein the firstuser-generated contour is displayed with a different visual appearancethan the extrapolated contours.
 16. The method according to claim 12,wherein the image planes of the first image planes set comprise parallelplanes.
 17. An apparatus for automatically generating a contour based ona user-modified contour in an image, the apparatus comprising: a memoryconfigured to store a plurality of contours disposed on a plurality ofstructures in a plurality of parallel planes; and a processor coupled tothe memory and configured to automatically update contours of astructure comprising the plurality of contours, responsive to user inputindicating modification of at least two contours of the plurality ofcontours, the at least two contours being disposed on at least twononadjacent and parallel planes of the plurality of parallel planes;wherein the processor is further configured to determine a first set ofplanes from the plurality of parallel planes disposed between the atleast two parallel planes; the processor further configured to determinean extrapolated contour on a third plane that is separated from the atleast two planes and the first set of planes by a second set of planes;and the processor further configured to automatically generateinterpolated contours on planes comprised by the second set of planes,the interpolated contours being based on the extrapolated contour. 18.The apparatus of claim 17, wherein a selection of differentinterpolation algorithms is provided.
 19. The apparatus of claim 17,wherein the processor is further configured, responsive to user input,to extrapolate one or more contours on one or more structure planesadjacent to a boundary structure plane having a contour.